XSAN 3.0 Client & XSAN 2.1 MDC

We currently deploy an XSAN system with 4 client machines (Mac Pro towers) and 1 MDC Server (Apple XServe Early 2008).

The Xserve cannot be upgraded past 10.7.5 OS - and therefore we have all our clients running 10.7.5. However, we have come across a new software we need to install on a client that only runs on 10.8 and above.

Has anyone successfully ran a client on 10.8 (with XSAN 3.0) but maintained the MDC on 10.7 (XSAN 2.3). Obviously, this is not supported in Apple's documents - but I was wondering if it was physically possible.

The alternative, of course, is to deploy a MacMini and replace the Xserve. Does anyone have a best practice to switch over (XSAN control, Open Directory, DNS, AFP) to a new MDC to replace the old one? We currently only have one MDC - no backup.